What qualifies a Voice Assistant to be an AI?
Usually, this sort of encoded 1to1 response is not considered to be AI or ML. This is because a chatbot that simply responds to a designated string with a response string is hard programmed(for the most part). A lot of companies/individuals have tried to package this as true AI but it is not.

One of the simpler examples of an AI chatbot system is a model that does some sort of tree-search or similar for the input. This is more often than not, extremely naive but would be an example of a true AI system.

So to more concisely answer your question, the categorization as an AI chatbot would have less to do with the responses, and more to do with how the model selects/comes up with those responses.